(461b) Bimetallic Nanoparticles Synthesis in Membrane Matrix: Nanoparticle Structure and Reactive Properties

In this study, nanosized core-shell Fe/Pd particles were synthesized in the polyacrylic acid (PAA)/polyvinylidene fluoride (PVDF) composite membranes. The PAA/PVDF membranes were prepared by a dip-coating process. The carboxylic groups in PAA layer bind ferrous ions from aqueous solution by ion exchange at controlled pH (5~6). Subsequent reduction with sodium borohydride forms metallic Fe nanoparticles. The advantages of using PAA for nanoparticle synthesis are: prevention of particle agglomeration and control of particle size, recapture of dissolved Fe²⁺ or Fe³⁺ from solution, and easy regeneration of nanoparticles. The core-shell Fe/Pd nanoparticles can be achieved by a partial displacement reaction on Fe surface. The membranes and Fe/Pd nanoparticles were characterized by several electron microscopy techniques: scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The reactive properties are dependent on the bimetallic nanoparticle structure and distribution of Fe and Pd at nano domain. A specimen-drift-free EDS mapping system was performed in STEM to determine the two-dimensional element distribution inside the membrane matrix at nano scale. The interfacial structure of Fe core and Pd shell are studied in detail using HRTEM. The reactive properties of Fe/Pd bimetallic nanoparticles in PAA/PVDF membrane were investigated toward the reductive dechlorination of 2,3,2',5'-tetrachlorobiphenyl (TeCB) at room temperature. Complete destruction of TeCB (C₀ = 12 mg L^-1) by membrane-based Fe/Pd (Pd = 2 wt%) nanoparticles was achieved within 2 hours. Biphenyl was formed as the main product in the first hour and the only product after 2 hours. Chlorinated intermediates (trichlorobiphenyl, dichlorobiphenyl and chlorobiphenyl) which were observed in the first hour were also quantified. Reductive dechlorination of TeCB under convective flow mode and recapture of dissolved Fe²⁺ were also investigated in this paper. This research is supported by the NIEHS-SBRP program and by U.S. EPA ? STAR Program.